A structural analysis of the Co(0001) surface and the early stages of the epitaxial growth of Cu on it

Abstract

The epitaxial growth of copper on Co(0001) was investigated by combined quantitative LEED and STM, including the clean surfaces Cu(111) and Co(0001). The mode of growth is a modified Stranski–Krastanov type, i.e. pseudomorphic and approximately layer-like up to four monolayers of copper; later on, three dimensional islands develop. The stacking of the copper adlayers is exclusively fcc from the very beginning, whereby the ABAB stacking on a given terrace of the substrate is continued as ABABca. Since there are also terraces with an ABA stacking, fcc-twins (e.g. ABAcb) develop in the Cu films. Whilst in the submonolayer coverage regime of copper the cobalt substrate remains hcp stacked, films with more than about two copper layers are found to have induced a stacking fault in the substrate corresponding to a registry shift of the uppermost cobalt layer. As indicated by the analysis of a film slightly above one monolayer coverage, the registry shift seems to be triggered when the terraces of the substrate are fully covered by copper whereby the rearrangement of atoms probably starts at the step edges.